DOCSLIB.ORG

Using Ferrite Beads Keep RF out of TV Sets, Telephones, VCR's Burglar Alarms and Other Electronic Equipment

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Using Ferrite Beads Keep RF out of TV Sets, Telephones, VCR's Burglar Alarms and Other Electronic Equipment Using Ferrite Beads Keep RF Out of TV Sets, Telephones, VCR's Burglar Alarms and other Electronic Equipment RFI and TVI have been with us for a long time. Now we have microwave ovens, VCR's and many other devices that do wrong things when they pick up RF. There are several ways to tackle the problem but most of them involve opening the affected equipment and adding suppressor capacitors, filters, and other circuit modifications. Unfortunately there is a serious disadvantage associated with this approach. Any modifications made to domestic entertainment equipment can - and often are - blamed for later problems that arise in it. Modifying your own equipment is not so bad, but taking a soldering iron to your neighbor's stereo is risky. An alternative approach is to use ferrite beads to reduce the amount of RF entering the equipment. If the equipment is in a metal box, or even if it's in a plastic box, if RF is prevented from entering the box on the antenna lead, the power cable, the speaker leads, the phono pickup leads, and on any other wires entering the box, it is possible to solve the problem without any modification to the equipment. Ferrite beads just slip over the wires and stop RF from going in. Ferrite beads are made of the same materials as the toroid cores used in broadband transformers but are used at much higher frequencies. For example, ferrite Mix 43 is used for tuned circuits in the frequency range 0.01 to 1 MHz. It is efficient and losses are low. But, if it is used in the 1-1000 MHz range it is lossy. So when you slip a bead of Mix 43 over a wire and there is RF in the 1 -1000 MHz range going down the wire, it is just as though you put a resistor in the wire. But you did not have to cut the wire to insert the resistor; you just slip a bead over the wire. If the resistance of one bead is not enough you can add more beads or add longer beads to get more resistance. The beads, unlike a resistor, do not affect the wire at low frequencies so the audio, DC, and other low frequency components go through the wire just as though the bead were not there. There are three bead materials in general use: Mix 77, Mix 43, and Mix 64. Mix 43 is the best for all-round use. It works from 1 to 1000 MHz. Mix 77 is a little better at the lower frequencies, so if your major problems are on 80 and 160 meters use it. Mix 64 is a little better on the higher frequencies so if your problems are mostly on two meters and up use it. It is important to remember that the frequencies mentioned are those of the interfering signals to be eliminated, not the operating frequencies of the equipment being protected. For example: To protect a telephone operating at voice frequencies of 0.002 MHz we use type 43 or 77 beads to keep 14 MHZ RF out. So when you buy beads you must specify both the physical size (FB-3, FB-8, etc.) and the material (Mix 77, Mix 43, etc.) depending on the frequency of the RF interference. FB-1, FB-3, and FB-7 have 0.05" holes that will slip over bare #18 gauge wire. FB-8 has a 0.09" hole and will slip over the insulation of #22 wire. FB-24 and FB-63 have 0.2" holes to go over larger wire or cable. FB-56 has a 1/4" hole to clear RG58/RG-59/RG-58X. FB-102 and FB- 124 have 1/2" holes to clear RG-8/RG-11. Cables. So far we have talked about slipping beads over individual wires. But, in many cases, we are going to find two wire speaker cables, two wire or three wire power cables, twinlead antenna cable, and multi-wire control cables. Cable wires are close together and act just like a single wire as far as RF pickup is concerned. So the whole cable can go through the bead and this will suppress RF transmission through all the cable-wires. This is a lot easier than putting beads on each wire. Twinlead is a special case. If you put a bead on each wire you'll kill the TV signal. But if the whole twinlead goes through a single bead, the TV signal goes on through but the RF interference is suppressed by the bead. This is because the twinlead is a transmission line to the TV signal but looks like a single wire to the RF interference. This brings us to coaxial cable. The signal going through the coax is confined to the inside of the coax shield. But the outside of the shield acts just like any wire; it can pick up RF and that RF can be carried to the TV or monitor. Shield beads placed over the cable will suppress this interference. Toroids. When we start talking about slipping beads over coaxial cable and multi-wire cable we see that we may need beads with pretty big holes. Also, if the cable has a molded plug on the end (like some power cords, for example) the plug has to go through the hole and we may need a very big hole indeed. Fortunately a variety of ferrite toroid cores are available with holes as big as 1.4" diameter. They are not available in all the same materials as beads but in similar ones. As a guide when specifying toroids for RF suppression: Mix 43 is the best for all-round use. It works from 1 to 1000 MHz. Mix 77 is a little better at the lower frequencies, so if your major problems are 80 and 160 meters use it. Mix 61 is a little better on the higher frequencies so if your problems are mostly on two meters and up use it. After you put that big plug through the toroid hole you'll find that the toroid fits the cable very loosely. Don't worry. It will still work fine. If there is room to do it, loop the cable around and run it through the toroid again. Do this as many times as you can. Each turn is just like adding another toroid. And, using the big Mix 61 cores, you add an inductive choke where two turns is four times as good as one turn, three turns is nine times as good, etc. Split Beads. This is a new development to solve the problem of putting beads or toroids over cables that have big plugs on the end. They are beads that have been cut in half. You put the two halves over the cable and wrap them with tape to hold them together. The mating edges are polished smooth so the two halves mate very closely. They are available with center holes of 1/4" and 1/2' diameter. Also for flat computer cable 2 or 2-1/2" wide. It is important that the two halves of the split beads fit exactly together. So the 1/2" hole beads cannot be used for cables larger than 1/4". It does not matter if the cable is smaller than the hole. All split beads now available are of 43 material which is the best overall material for 1-1000 MHz interference suppression. Telephone Interference. The standard telephone is highly susceptible to RFI. The telephone wiring in the house and outside on poles make a large receiving antenna. And in the telephone instrument are voltage-variable resistors that act like detector diodes so nearby radio stations are clearly heard. The solution is to keep RF out of the telephone by putting ferrite beads on the telephone cable as it enters the instrument. The plug of modular telephones will go through F82 toroids. Unplug the wire from the telephone, put it through the hole of the toroid (three or four times if there is room) and plug it back into the telephone. Or use a split bead. Burglar Alarms. These are much like telephones in that they have extensive wiring throughout the building that acts like an antenna to pick up RF. The solution is the same: Use beads or toroids on the wire entering the electronics box to keep RF out. It also may be necessary to put beads on the 115-v AC power cord. TV Sets. Put a bead or toroid on the power cord as it enters the set. Toroids or split beads on the antenna cable also may be needed. VCR's. The VCR is a real RFI problem. Ferrite beads on all wires entering the VCR can eliminate RFI from most amateur bands. But on 80 meters even this doesn't always work. It may be necessary to shield the VCR housing to completely eliminate RFI. Stereo. Long speaker wires can act like an antenna to pick up RF and feed it into the output of the amplifier. The amplifier's feedback circuit allows the RF to reach the input where it is rectified, amplified and then heard in the speaker. The solution is to use beads on the speaker wires just as they leave the amplifier. RF can enter the stereo system through the power cord. Use a split bead or a toroid on the cord just as it enters the stereo. We have been talking about keeping RF out of equipment.
Load more

Recommended publications
  • Filtering and Suppressing Transients
    Another EMC resource from EMC Standards EMC techniques in electronic design Part 3 - Filtering and Suppressing Transients Helping you solve your EMC problems 9 Bracken View, Brocton, Stafford ST17 0TF T:+44 (0) 1785 660247 E:[email protected] Design Techniques for EMC Part 3 — Filtering and Suppressing Transients Originally published in the EMC Compliance Journal in 2006-9, and available from http://www.compliance-club.com/KeithArmstrong.aspx Eur Ing Keith Armstrong CEng MIEE MIEEE Partner, Cherry Clough Consultants, www.cherryclough.com, Member EMCIA Phone/Fax: +44 (0)1785 660247, Email: [email protected] This is the third in a series of six articles on basic good-practice electromagnetic compatibility (EMC) techniques in electronic design, to be published during 2006. It is intended for designers of electronic modules, products and equipment, but to avoid having to write modules/products/equipment throughout – everything that is sold as the result of a design process will be called a ‘product’ here. This series is an update of the series first published in the UK EMC Journal in 1999 [1], and includes basic good EMC practices relevant for electronic, printed-circuit-board (PCB) and mechanical designers in all applications areas (household, commercial, entertainment, industrial, medical and healthcare, automotive, railway, marine, aerospace, military, etc.). Safety risks caused by electromagnetic interference (EMI) are not covered here; see [2] for more on this issue. These articles deal with the practical issues of what EMC techniques should generally be used and how they should generally be applied. Why they are needed or why they work is not covered (or, at least, not covered in any theoretical depth) – but they are well understood academically and well proven over decades of practice.
    [Show full text]
  • Chapter 21 Some Aspects of the Balun Problem
    Chapter 21 Some Aspects of The Balun Problem (Adapted from QST, March 1983) type baluns which prove that with a 50-ohm resis• tive load, the transformers in typical 1:1 or 4:1 Sec 21.1 Introduction baluns do not yield a true 1:1 or 4:1 impedance transfer ratio between their input and output termi• nals. This is because of losses, leakage reactance, hy all the mystery surrounding baluns? and less than optimum coupling. My findings have Here's some straight talk to dispel the been substantiated by the work of the late John rumors! The balun—to use, or not to W Nagle, K4KJ (Ref 80). Furthermore, the imped• use—is one of the hottest topics in amateur radio. ance-transfer ratio of such baluns degrades even Because certain aspects of the connection between a further when used with an antenna that is reactive coaxial feed line and a balanced antenna have been from operation away from its resonant frequency. ignored, misunderstanding still exists concerning This degradation of impedance transfer associated the function of baluns. Many commercial baluns with transformer-type baluns poses no serious embody some form of impedance transformer, pro• operational problems. However, SWR curves plot• moting our tendency to misconstrue them as little ted from measurements of an antenna using such a more than a matching device, while their primary balun differ significantly from those using a choke function is to provide proper current paths between balun that has no impedance-transfer error. Thus, balanced and unbalanced configurations. when a precision bridge is used to measure anten• To help clarify the misunderstanding, this chap• na impedance (R + y'X), the data will be erroneous ter explains some of the undesirable effects that with either a transformer-type balun in the circuit, occur when a balun is not used, and some that or with no balun at all.
    [Show full text]
  • Variable Capacitors in RF Circuits
    Source: Secrets of RF Circuit Design 1 CHAPTER Introduction to RF electronics Radio-frequency (RF) electronics differ from other electronics because the higher frequencies make some circuit operation a little hard to understand. Stray capacitance and stray inductance afflict these circuits. Stray capacitance is the capacitance that exists between conductors of the circuit, between conductors or components and ground, or between components. Stray inductance is the normal in- ductance of the conductors that connect components, as well as internal component inductances. These stray parameters are not usually important at dc and low ac frequencies, but as the frequency increases, they become a much larger proportion of the total. In some older very high frequency (VHF) TV tuners and VHF communi- cations receiver front ends, the stray capacitances were sufficiently large to tune the circuits, so no actual discrete tuning capacitors were needed. Also, skin effect exists at RF. The term skin effect refers to the fact that ac flows only on the outside portion of the conductor, while dc flows through the entire con- ductor. As frequency increases, skin effect produces a smaller zone of conduction and a correspondingly higher value of ac resistance compared with dc resistance. Another problem with RF circuits is that the signals find it easier to radiate both from the circuit and within the circuit. Thus, coupling effects between elements of the circuit, between the circuit and its environment, and from the environment to the circuit become a lot more critical at RF. Interference and other strange effects are found at RF that are missing in dc circuits and are negligible in most low- frequency ac circuits.
    [Show full text]
  • Differential and Common Mode Noise Differential and Common Mode Noise 26
    This is the PDF file of text No.TE04EA-1. No.TE04EA-1.pdf 98.3.20 4. Other Filters 4.1. Differential and Common Mode Noise Differential and Common Mode Noise 26 ■ Differential mode noise ■ Suppression method of differential mode noise Signal Signal source source Load Noise Noise Load source N source N ■ Common mode noise ■ Suppression method of common mode noise (1) Signal Stray source capacitance Signal Suppresses noise. Stray source capacitance Noise source Load Noise N source N Load Stray Stray capacitance capacitance Reference ground surface Reference ground surface ■ Suppression method of common mode noise (2) Signal source Noise Load source N Line bypass capacitor Metallic casing Reference ground surface Noise is classified into two types according to the conduction are installed on all lines on which[Notes] noise is conducted. mode. In the examples shown above, the following two suppression The first type is differential mode noise which is conducted on methods are applied. the signal (VCC) line and GND line in the opposite direction to 1. Noise is suppressed by installing an inductor to the signal line each othe. This type of noise is suppressed by installing a filter on and GND line, respectively. the hot (VCC) side on the signal line or power supply line, as 2. A metallic casing is connected to the signal line using a mentioned in the preceding chapter. capacitor. Thus, noise is returned to the noise source in the The second type is common mode noise which is conducted on following order; signal/GND lines ➝ capacitor ➝ metallic all lines in the same direction.
    [Show full text]
  • Use of Ferrites in EMI Suppression
    The Use Of Ferrites In EMI Suppression USE OF FERRITES Properties Of Ferrites Introduction Ferrites are a class of ceramic ferromagnetic ma- 600 ohms, and becomes essentially resistive above terials that by definition can be magnetized to 100 MHz. When used as EMI filters, ferrites can produce large magnetic flux densities in response thus provide resistive loss to attenuate and dissi- to small applied magnetization forces. Originally re- pate (as minute quantities of heat) high frequency ferred to as “magnetic insulators,” ferrites were first noise while presenting negligible series impedance used as replacements for laminated and slug iron to lower frequency intended signal components. core materials in low loss inductors intended for use When properly selected and implemented, ferrites above 100 kilohertz (kHz). At these frequencies, can thus provide significant EMI reduction while re- laminated and slug iron are plagued by excessive maining “transparent” to normal circuit operation! For eddy current losses whereas the high volume re- high frequency applications, ferrites should be sistivity of ferrite cores limit power loss to a fraction viewed as frequency dependent resistors. Since of other core materials. Today, Steward ferrites are they are magnetic components that exhibit signifi- the core material of choice for modern high density cant (and useful) loss over a bandwidth of over 100 switch mode power supply and pulse transformer MHz, ferrites can be characterized as high fre- design. quency, current operated, low Q series loss elements. Whereas a purely reactive (i.e., com- Fundamental Properties posed only of inductors and capacitors) EMI filter While frequently nicknamed “magic beads” in may induce circuit resonances and thus establish marketing literature, EMI suppression ferrites are additional EMI problem frequencies, lossy ferrites actually well understood magnetic components.
    [Show full text]
  • Shielding of Electronic Traffic Control Equipment
    l l 1 I i l I i l l NATToNAL coopERArrvE HrcHwAy RESEARcH ri::ååi 317 TRANSIENT PROTECTION, GROUNDING, AND SHIELDING OF ELECTRONIC TRAFFIC CONTROL EQUIPMENT H. W. DENNY and J. p. ROHRBAUGH Georgla Tech Research lnstitute Georgia lnstitute of Technology Atlanta, Georgia RESEARCH SPONSORED BY THE AMERICAN ASSOCIATION OF STATE HIGHWAY AND AREAS OF INTEREST: TRANSPORTATION OFFICIALS IN COOPERATION WITH THE FEDERAL HIGHWAY ADMINISTRATION Maintenance operations and Traffic Control (Highway Transportation) TRANSPORTATION RESEARCH BOARD NATIONAL RESEARCH COUNCIL WASHINGTON, D.C, JUNE 1989 NATIONAL COOPERATIVE HIGHWAY RESEARCH NCHRP REPORT 317 PROGRAM Project 10-34 FY'86 Systematic, well-designed research provides the most effec- ISSN 0077-5614 tive approach to the solution of many problems facing high- ISBN 0-309-04ó14-9 way administrators and engineers. Often, highway problems L. C. Catalog Card No. 89-50190 are of local interest and can best be studied by highway de- partments individually or in cooperation with their state universities and others. However, the accelerating growth Price $11.00 of highway transportation develops increasingly complex problems of wide interest to highway authorities. These NOTICE problems are best studied through a coordinated program of The project that is the subject of this report was a part of the National Co- operative Highway Research Program conducted by the Transportation Re- research. cooperative search Board with the approval of the Goveming Board of the National Research Council. Such approval reflects the Governing Board's judgment In recognition of these needs, the highway administrators of thât the program concemed is of national importance and appropriate with the American Association of State Highway and Transpor- respect to both the purposes and resourcc of the National Research Council.
    [Show full text]
  • Or Ferrite Beads  Ferrite Is a Magnetic Material Designed for Use at Radio Frequencies Ferrite Beads
    HF OPERATORS - • - • -- • -- • • • • • • - • -- • • • - • • • • • - • WHY YOU NEED A CURRENT BALUN by John White VA7JW 10/27/2014 NSARC HF Operators 1 What is a Balun ? - • - • -- • -- • • • • • • - • -- • • • - • • • • • - • A BALUN is a device typically inserted at the feed point of a dipole-like antenna wire dipoles, Yagi’s, quads, loops etc. Vertical antenna usage possible but not discussed here Provides an interface between the coax feed line and the antenna feed point 10/27/2014 NSARC HF Operators 2 What Does It Look Like - • - • -- • -- • • • • • • - • -- • • • - • • • • • - • Typically a cylindrical tube or a rectangular box Has supporting eye bolts Antenna connection terminals Coax cable connector All very handy Supporting Eye-Bolt Eye-Bolts for Antenna wire connection Coax Connector 10/27/2014 NSARC HF Operators 3 Two Types of Balun - • - • -- • -- • • • • • • - • -- • • • - • • • • • - • Two types of Baluns, Electrically different Look identical outwardly The Current Balun – is the topic of discussion The Voltage Balun – is not useful for resolving the problems presented here Ensure the balun label states it is a current balun. If a balun is to remedy issues discussed herein, it must be a Current balun 10/27/2014 NSARC HF Operators 4 What’s Inside - • - • -- • -- • • • • • • - • -- • • • - • • • • • - • A transformer-like structure using a ferrite “core”, or ferrite beads Ferrite is a magnetic material designed for use at radio frequencies Ferrite Beads Windings on different styles of ferrite cores Threaded on coax cable 10/27/2014 NSARC HF Operators 5 What Does It Do? - • - • -- • -- • • • • • • - • -- • • • - • • • • • - • 1. Matches a BALanced antenna to UNbalanced coax connection, hence the name BAL-UN 2. Provides impedance matching between coax characteristic Z and antenna feed point Z 3.
    [Show full text]
  • Hidden Antennas & Ferrite Beads
    <CD "m 0 Z Hidden Antennas & Ferrite Beads ~ CD :::J ;v ~ :>- --+ ,z • CD ith all the various deed restrictions and s covenants out there, many of you have a :>- :::J few problems putting up a lower and a ;!.' W L :::J triband beam. Back in my Novice days. my first CD antenna was a 40·meter folded dipole made of out recycled twinlead from a neighbor's old TV anten­ 0 na, stapled to the ratters inside my parents' attic. en I even had some teenage notion that a 40-meter folded dipole would also work on 80 meters, but many hours 01 pounding out CO without an answer (the only crystal I owned was 3720 kHz) convinced me I was wrong about folded dipoles. A lew years later I took an old conical TV antenna. added 6 inches 10 the elements. put it up in the attic, and made my first e-rneter AM contacts. Up In the Allie Today, attic antennas are still one way of staying on the air. In photo A. we are using a mobile anten­ Photo A- Using a mobile antenna in the attic. Just na mount (see several options in photo B) and one keep headroom issues in mind. especially with of the · s t i ck ~ type mobile whips chosen for your motorized multiband antennas. favorite band. The base is made from a couple of piecesof aluminum Lsection,each two to three feet long. Certainly there's a lot of other stuff you can more than one band. There are two ways to multi­ use; you just need something electrically conduc­ band this ground plane.
    [Show full text]
  • A Few Chosen Topics John Kernkamp – WB4YJT Tonight’S Topics
    Antennas A Few Chosen Topics John Kernkamp – WB4YJT Tonight’s Topics • Baluns • RF Safety • Discone Antennas • Secret Topic Baluns • The word is a conflation of “Bal anced” and “Un balanced”. • Coax cable is “Unbalanced” • A dipole is “Balanced” • A Ground-mounted Vertical is “Unbalanced” Balun Purpose • Prevents RF current on feedline RF on the feedline will distort the antenna’s pattern RF on the feedline can come into the shack and cause problems • Matches feedline to antenna 1:1 for 50/75 Ohm antenna 4:1 for 300 Ohm antenna 6:1 for higher impedances Types of Baluns • Coax • Choke • Ferrite Bead • Ferrite Core • Transmission-Line Transformer Coax Balun • A length of coax to give an electrical half-wave delay to the drive for one element • Provides 4:1 Impedance change • Single-frequency Choke Balun • Simply a coil of the feedline coax to create an inductance which will prevent RF on the outside of the feedline • A 1:1 Balun, broadband Ferrite Bead Balun • Ferrite beads create inductance on the outside of the feedline, which blocks RF • A 1:1 Balun, broadband • Different bead material for VHF/UHF, and for HF Ferrite Characteristics Ferrite Balun Kits High Sierra, Amidon, Palomar, Hex Kit, Wireman, Elecraft Transformer Baluns • C. L. Rutheroff first outlined designs for transmission line transformers in his paper "Some Broadband Transformers", published in Proceedings of the IRE, Volume 47, August 1959. • These transformers had very wide bandwidth characteristics, some as high as 20,000:1. Frequencies ranged from a few tens of kilohertz to over one gigahertz. Transformer Baluns • Jerry Sevick – W2FMI (SK) built on Rutheroff’s concepts and published “Transmission Line Transformers” in 2001.
    [Show full text]
  • Practical EMI Filter Design Workshop IEEE 2008 Detroit
    Capacitor Practical EMI Filter Design Workshop IEEE 2008 Detroit Alexander Gerfer & Michael Eckert FR-PM-3 FR-PM-3 Capacitor : Equivalent Circuit Impedance vs. Frequency of Capacitors Inductance of connection: ESR: SMD-types 1 nH ... 5 nH SMD-types 20 mΩ ... 300 mΩ wired 10 nH ... 50 nH ! up to 1 Ω (see Datasheet ) FR-PM-3 FR-PM-3 978-1-4244-1699-8/08/$25.00 ©2008 IEEE Simulation Datas for Caps from Î KEMET Spice Simulation Datas for Caps from Î KEMET Spice FR-PM-3 FR-PM-3 Capacitance: DC-Bias and Temperature Capacitor : KEMET Spice Simulation Model Capacitance decrease temperature increase (@ = 0VDC Î 18 µF !!) Capacitance decrease by DC-bias !!! Effective only Î 8.6 µF !! C0805C104K3RAC @ 25°C, 0VDC, 41,687 kHz Î LTspice www.kemet.com www.linear.com FR-PM-3 FR-PM-3 Pratice-Tip: SRF of SMD-Capacitors What is an Inductor ? Example 1: Filter with maximum attentuation at f = 500 MHz in a system ZA = ZB = 100 Ω = konst.; T-Filter Step 1: choose C with SRF @ 500 MHz => Nomogramm: size 1206 ; C = 68 pF Step 2: SRF [MHz] SRF calculation of Ls „Headache-Parts“ ?! A mystery......... SRF = 500 MHz : = 1 = L S ⋅ 2 1,49 nH C S ω res 68 pF Capacitance [pF] FR-PM-3 FR-PM-3 What is an Inductor ? What is an EMC-Ferrite ? technical view: technical view: a piece of wire wounded on something Absorber for RF a filter frequency dependent filter an energy-storage-part (short-time) examples: examples: EMC Snap-Ferrites EMC-Ferrites for SMD-Ferrite Flatwire WE-CBF FR-PM-3 FR-PM-3 The basics of Inductive Components The basics of Inductive Components Magnetic
    [Show full text]
  • Transmission Line, Power and Protection Considerations for the LWA Antenna System Whitham D
    Transmission Line, Power and Protection Considerations for the LWA Antenna System Whitham D. Reeve 1. Introduction This document provides application details for the Long Wavelength Array antenna system. The LWA antenna system consists of two major assemblies, the crossed-dipole antenna elements and associated support structure, and the active balun assembly (also called Front End Electronics, or FEE) consisting of two active balun printed circuit boards, one for each dipole (figure 1). Each active balun has approximately 35 dB gain in the frequency range 10 to 100 MHz and is located in the enclosure at the top of the antenna assembly. The active baluns are powered through their respective coaxial cable transmission lines and bias-tees. The LWA antenna is a part of a system that includes other interfaces and power supplies (figure 2). Figure 1 ~ LWA antenna consists of two major assemblies, the mechanical structure and electronics (dual active balun assembly). The dual active balun assembly is in the enclosure at top of the antenna. The ground stake at the bottom of the center post anchors the antenna in earth. The horizontal components from the center post to the antenna blades and between blades are non-conductive mechanical supports. (Image © 2014 W. Reeve) 2. Transmission Considerations The LWA antenna is a 50 ohm system. Some users may attempt to employ 75 ohm coaxial cable, but comparative measurements have not yet been made to determine if there is performance degradation. Also, using 75 ohm cables inevitably leads to impedance mismatches and the need for RF adapters, and these should be avoided wherever possible.
    [Show full text]
  • Grounding and Bonding for the Radio Amateur ARRL.Pdf
    Copyright © by The American Radio Relay League, )nc. Copyright secured under the Pan-American Convention All rights reserved. No part of this work may be reproduced in any form except by written permission of the publisher. All rights of translation are reserved. Printed in USA Quedan reservados todos los derechos )SBN: ---- First Edition eBooks created by www.ebookconversion.com We strive to produce books without errors. Sometimes mistakes do occur, however. When we become aware of problems in our books other than obvious typographical errors, we post corrections on the ARRL website. )f you think you have found an error, please check www.arrl.org/notes for corrections. )f you dont find a correction there, please let us know by sending e-mail to [email protected]. CONTENTS Preface About ARRL Chapter — )ntroduction . What Are Grounding and Bonding? . Materials — An )ntroduction . Techniques and Tools — An )ntroduction . Things to Find Out Chapter — Grounding and Bonding Basics . Using the Right Term . )mportant Standards and Guidelines Chapter — AC Power System Grounding and Bonding . Safety First — Always . Shock (azards . Power System Grounding and Bonding . AC Safety Grounding Specifics . AC Power in Your Station Chapter — Lightning Protection . What is Lightning? . Controlling Current Paths . Protecting Against Voltage Transients . Bonding to Equalize Voltages Chapter — RF Management . Your Station, the RF System . RF Fundamentals . Bonding to Equalize Audio and RF Voltage . Blocking RF Current with Chokes . Miscellaneous Topics Chapter — Good Practice Guidelines . Ground Electrodes . AC Power . Lightning Protection Planning . Managing RF in the Station . Practical Stations Appendix Resources for )nformation and Materials Material Sizes and Values Wiring for V and V ac Plugs and Outlets Common-Mode Chokes and Ferrite Characteristics Glossary PREFACE This book is largely a distillation of expertise contributed by others, both professional and amateur.
    [Show full text]